🤖 Calculating the Self-Attention mechanism in pure PyTorch.

The Attention Mechanism allows transformer neural networks to determine the connection between words in a text and dynamically focus on the most important context. We will step by step implement the basic algorithm Scaled Dot-Product Attention, using classic matrices of queries (Query), keys (Key) and values (Value). This will help us to visually see how the attention weights are mathematically calculated and how the model matches the tokens with each other. 🧠✨

To start, we will install the PyTorch library for performing tensor calculations. 🛠️

pip install torch

The library has been successfully loaded and is ready for mathematical modeling of transformer layers. ✅

We will generate random vectors Query, Key and Value to simulate the passage of tokens through linear projections. 🎲

import torch
import torch.nn.functional as F

q = torch.randn(1, 3, 4)  # (batch, seq_len, dim)
k = torch.randn(1, 3, 4)
v = torch.randn(1, 3, 4)

The tensors have been initialized and represent three hidden states for a sequence of three words. 📝

We will calculate the token similarity matrix through the scalar product and then scale it by the square root of the vector dimensions. 🔢

scores = torch.bmm(q, k.transpose(1, 2)) / (q.shape[-1] ** 0.5)
attention_weights = F.softmax(scores, dim=-1)
output = torch.bmm(attention_weights, v)

The scalar product has been translated into probability weights, based on which the final contextual vector has been formed. 🔄

A control run of the output dimension calculation:

python3 -c "import torch; q, k = torch.randn(1, 3, 4), torch.randn(1, 3, 4); print('Attention OK') if torch.bmm(q, k.transpose(1, 2)).shape == (1, 3, 3) else print('Error')"

Expected output: Attention OK ✅

The Self-Attention formula lies at the heart of all modern LLMs, allowing them to process long contexts in parallel, unlike old recurrent networks (RNNs). Understanding this base is critically important for working with transformers, optimizing architectures and configuring KV-cache mechanisms. 🚀🧠

#PyTorch #Transformer #DeepLearning #AI #MachineLearning #LLM

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